1. Field of the Invention
The present invention relates to a magnetic field sensor which is provided with a magnetic field detecting element for detecting an external magnetic field change and, in particular, to a magnetic field sensor for detecting rotation and position.
2. Description of the Prior Art
(1) A magnetoresistance effect element is an element for measuring a magnetic field intensity by using a phenomenon (magnetoresistance effect, i.e., MR effect) in which an electric resistance of a ferromagnetic metal changes with an external magnetic field change. For a single-layer magnetic film, a heretofore known anisotropic magnetoresistance effect has been used. Recently, as disclosed in, for example, publications of patent application laid-open Nos. Hei 5-259530 and 7-77531, another element is developed by using a giant magnetoresistance effect (hereinafter referred to as the GMR effect) of a magnetic film with a multilayered structure.
Also, as introduced in National Technical Report, Vol. 42, No. 4, pp. 465-472, a VTR capstan motor rotation detecting sensor uses a NiFeCo/Cu multilayered film as a GMR effect element. By detecting a magnetic field change from a multipolar magnetic rotor, the magnetic field sensor, as a result, detects a rotational speed in a non-contact manner. Therefore, in this magnetic field sensor, it is very important to minimize a distance (gap) of the magnetoresistance effect film as a detecting portion from the magnetic rotor. For this, the technical report discloses a structure in which inside through holes formed in an alumina substrate AgPd are used to print an electrode draw portion on a rear face of a substrate. Also, in a magnetic field sensor using Hall element which is introduced in National Technical Report, Vol. 42, No. 4, pp. 480-488, to realize a surface mounting thickness of 200 .mu.m or less, TAB (tape automatic bonding) mounting is performed on a substrate with a magnetic field detecting element formed thereon, to draw an electrode by using a CU foil lead. However, in such a conventional method, process is complicated, thereby increasing cost.
Also, in Japanese Applied Magnetics Journal, 1992, Vol. 16, pp. 643-648 it is described that in a conventional magnetic field detecting element constituted of a magnetic thin film deposited on a hard substrate since a magnetic property of the magnetic film changes with a magnetic elasticity effect produced by an unavoidable stress from the substrate or a protective film, various attempts are necessary when the change is considered. Especially, a thermal stress is an important factor which influences the magnetic property. By sufficiently considering a film-forming temperature and an operation temperature, the magnetic element needs to be designed. Further, the magnetic property of magnetoresistance effect film often needs to be finely optimized in accordance with various product specifications. As a result, products are diversified, thereby complicating a process control.
(2) As aforementioned, National Technical Report, Vol. 42, No. 4, page 465 introduces the VTR capstan motor rotation detecting sensor which uses the NiFeCo/Cu multilayered film as the GMR effect element.
Also, as a prior-art magnetic field detecting element, the publication of patent application laid-open No. Hei 7-77531 discloses a magnetic position detecting element and a rotation detecting element,in which a magneto-sensitive pattern using a GMR effect is disposed at a magnetic-field pitch .lambda./2 or .lambda./4 of a detected body.
As another prior-art magnetic field detecting element, a publication of patent application laid-open No. Hei 1-297508 discloses a magnetic sensor in which four magneto-sensitive patterns are disposed to have a constant relationship with a magnetic-field pitch of a detected body.
Plural magneto-sensitive patterns are disposed so as to have a predetermined relationship with the magnetic-field pitch of the detected body. A differential magnetic field detecting element constituted in this manner is heretofore known broadly.
However, for example, as shown in FIG. 25, a magnetic field detecting element 100, which is heretofore proposed as aforementioned, is constituted of two thin-film patterns (magneto-sensitive pattern portions) 111 and 115 for detecting a magnetic field. These films are formed on a substantially flat common substrate (e.g., wafer substrate) 110 with a predetermined distance D therebetween which is determined by considering a magnetic-field pitch of a detected body. Numeral 120 denotes electrode pads for applying a current.
According to the prior-art constitution, however, for the purpose of making multiple magnetic field detecting elements 100, when plural magnetic field detecting elements 100 are formed altogether on the wafer substrate having a constant area, the number of magnetic field detecting elements 100 which can be deposited on the wafer substrate cannot be increased.
Also, when there are plural types of magnetic-field pitches of the detected body, the magneto-sensitive patterns need to be disposed and formed with different intervals formed thereamong in accordance with the magnetic-field pitches. To form the patterns on the magnetic field detecting element 100, masks and the like must be prepared beforehand in accordance with the magnetic-field pitches. Therefore, various types of masks and the like are necessary for each of the multiple detected bodies.
Also, the conventional magnetic field detecting element 100 has the following operational problem. To depict the problem, FIG. 24 shows an operation example of the conventional magnetic field detecting element 100. The magnetic field detecting element 100 is dispose spaced from the teeth of soft magnetic body rotary gear 160 as illustrated in FIG. 24. On the magnetic field detecting element 100 a permanent magnet 170 is disposed. A magnetic flux from the permanent magnet 170 changes with a positional relationship with the rotary gear 160. The condition of the change is detected by the magneto-sensitive pattern portions 111 and 115 which are formed with the predetermined interval D therebetween. In this case, the direction of a variation in magnetic-field pitch is, i.e. the smaller pattern line widths Pw of the magneto-sensitive pattern portions 111 and 115 in an x-direction in which the rotary gear 160 rotates are, the better. This is because a differential operation is preferable at a point where a difference in magnetic field to be detected is the largest. However, in the conventional magnetic field detecting element 100, as shown in the drawing, since the pattern line is folded plural times, an actual magnetic field detecting region is distributed in the x-direction. Therefore, if the magnetic-field pitch of the detected body is narrow, the magnetic field to be originally detected cannot be detected in some case.
(3) As aforementioned, the magnetic field sensor is a device for converting an external magnetic field change into an electric signal, and is constituted by patterning a ferromagnetic body and a semiconductor thin film to form an element which converts the external magnetic field change as a voltage change into the electric signal when a current is applied to the thin-film pattern. For example, the magnetoresistance effect film measures a magnetic field intensity using a phenomenon (MR effect) in which the electric resistance of a ferromagnetic metal changes with the external magnetic field. For the single-layer magnetic film, a heretofore known anisotropic magnetoresistance effect of the ferromagnetic metal film has been used. Recently, however, the GMR effect element constituted of the multilayered film structure has been reported. For example, as introduced in National Technical Report, Vol. 42, No. 4, page 465, the VTR capstan motor rotation detecting sensor uses a NiFeCo/Cu multilayered film as the GMR effect element. Also, in National Technical Report, Vol. 42, No. 4, page 84 disclosed is a semiconductor magnetic field detecting sensor which uses an InSb thin film.
A general structure of a heretofore used magnetic field sensor is shown in FIG. 26. As shown in FIG. 26, on one face 210a of a substrate 210 formed are a thin-film pattern 220 for detecting a magnetic field and electrodes 230 interconnected thereto. Further on these elements, a protective film 208 is disposed for protecting the elements. In the structure, the protective film 208, i.e. the substrate face 210a with the thin-film pattern 220 formed thereon is opposed to a detected body 270. Further, in the conventional magnetic field sensor, through holes 233 are formed in the substrate 210. Via conductive bodies 233a filled in the through holes 233, portions are solder-bonded and lead wires 235 are connected to a rear face 210b of the substrate 210 through bonds 234. In this manner, by minimizing a distance G1 between the thin-film pattern 220 and the detected body 270, a sensitivity is improved. If the solder-bonded portions and the lead wires are exposed on the surface of the substrate 210, the distance G1 cannot be minimized.
However, the structure provided with the through holes 233 and the protective film 208 formed on the thin-film pattern 220 is remarkably complicated, thereby deteriorating the productivity and increasing the manufacture cost. Further, to improve the sensitivity, the protective film 208 cannot be formed very thick. Also the formed protective film 208 itself is not very rigid. In some case there arises a problem with respect to weatherability. Additionally, in FIG. 26 numeral 260 denotes a permanent magnet, which is filled and sealed with a resin 261 in a shield case 265.
Another prior art of the invention is disclosed in a publication of patent application laid-open No. Sho 63-196874. The publication discloses a magnetoresistance effect sensor provided with a thin-film pattern formed on a surface of a substrate for detecting a magnetic field. On the other hand, a rear face of the substrate is used as a detecting face which is opposed to a detected body. According to the prior art, connected portions are prevented from rising or otherwise. Therefore, the distance from the detected body can be minimized and the sensitivity is increased. Further, the sensor can be manufactured with good yield and inexpensively.
However, the substrate disclosed in the patent application laid-open No. Sho 63-196874 is a glass substrate, which is relatively easily broken. An originally thin glass substrate cannot be used. Therefore, after a magnetic-field detecting thin-film pattern is once formed on a relatively thick substrate, a rear face of the glass substrate needs to be processed thin by grinding, polishing and etching. The process is remarkably laborious. Also, since the processed glass substrate is thin, its mechanical strength is unstable. The glass substrate may still be broken by a slight vibration or the like during the process. Further, in the prior art, no measure is taken for radiating heat which is generated in the magnetic-field detecting thin-film pattern during operation.
(4) As aforementioned, the magnetic field sensor converts the external magnetic field change into the electric signal. By patterning the ferromagnetic body, the semiconductor thin film or another magnetic field detecting thin film and applying a current to the thin-film pattern, the external magnetic field change is converted as the voltage change into the electric signal.
For example, the ferromagnetic magnetoresistance effect sensor measures a magnetic field intensity by using the phenomenon (MR effect) in which the electric resistance of the ferromagnetic metal changes with the external magnetic field.
For the single-layer magnetic film, the heretofore known anisotropic magnetoresistance effect of the ferromagnetic metal film has been used. Recently, as disclosed in the publications of patent application laid-open Nos. Hei 5-259530 and 7-77531, also developed is a magnetic field sensor which uses a combined type of great magnetoresistance effect (GMR effect) of a magnetic film with a multilayered structure.
Also, as introduced in National Technical Report, Vol. 42, No. 4, page 465, the VTR capstan motor rotation detecting sensor uses the NiFeCo/Cu multilayered film as the GMR effect element.
The GMR effect film is usually formed on a hard substrate of silicon, glass or the like. However, in Appl. Phys. Lett. (69) pp. 3092-3094 (1996), another attempt is described in which a spin valve structure film exhibiting a GMR effect is formed on an organic film. As compared with the hard substrate, the organic film is less expensive and can be easily cut, separated or processed otherwise when forming an element. The organic film advantageously contributes largely to a reduction in manufacture cost.
The present known GMR effect film is largely classified into 1 an antiferromagnetic-coupled type having a ferromagnetic body/nonmagnetic conductor structure, 2 an induction ferri (non-coupled) type having a high coercive-force ferromagnetic body/nonmagnetic conductor/low coercive-force ferromagnetic body structure, 3 a spin valve type having an antiferromagnetic body/ferromagnetic body/nonmagnetic conductor/ferromagnetic body structure and 4 a Co/Ag non-solid solution system granular type.
These GMR effect films are largely different from one another in magnetic field intensity to be detected, i.e. the saturation magnetic field intensity of the magnetoresistance effect, because of their structures and compositions. Therefore, when designing an actual GMR effect film, to obtain a maximum magnetic sensitivity in accordance with the magnetic field intensity to be detected, first a basic form is selected from various GMR effect films. Then, the composition system needs to be modified and further a fine structure thereof needs to be optimized.
Among the above GMR effect films, 1 the antiferromagnetic-coupled type having the ferromagnetic body/nonmagnetic conductor structure or 2 the induction ferri (non-coupled) type having the high coercive-force ferromagnetic body/nonmagnetic conductor/low coercive-force ferromagnetic body structure is so-called a GMR effect multilayered film. By laminating 10 to 100 layers of remarkably thin films with a layer thickness of 10 nm or less, a large magnetoresistance effect can be obtained.
In contrast, because the above 3 spin valve type uses a resistance change along a spin direction between two magnetic layers, the thickness of each magnetic layer exceeds 10 nm. Since this type has a small number of layers, it is also called a sandwich type. The aforementioned GMR effect film disclosed in the AppI. Phys. Lett. (69) pp. 3092-3094 (1996) is of the spin valve type.
The aforementioned 1 coupled type or 2 induction ferri-type GMR effect multilayered film has an appropriate detection magnetic field value of several hundreds of Oe. Therefore, this film is preferably used as the magnetic field sensor. Also, as aforementioned, the organic film starts to be introduced as the substrate.
However, it has been remarkably difficult to form the GMR effect multilayered film with 10 to 100 layers each having a thickness of 10 nm or less laminated therein on the flexible substrate of resin and thus obtain a high MR change ratio. Specifically, the flexible substrate of resin has a much smaller thermal conductivity as compared with the hard substrate of silicon, glass or the like. When the GMR effect multilayered film is formed on the flexible substrate of resin by sputtering or another vacuum film-forming process, the surface of the substrate with the multilayered film actually formed thereon tends to have a high temperature even if the substrate is cooled from the rear face thereof. Therefore, constituent elements are diffused among the layers of the multilayered film during the film formation, and smooth interlayer faces cannot be obtained. This tendency or problem prominently arises especially when forming the GMR effect multilayered film which is obtained by laminating 10 to 100 layers of remarkably thin films having a layer thickness of 10 nm or less.